32 METALLURGY OF CAST IRON.
by bosh, tap, and flue cinder. Mill cinder is generally used first because it can often be purchased for about one-half the price of iron ore and because it often contains a large percentage of iron.
Tap cinder is of two varieties, one is " boilings'* that flow over the floor plate of a puddling furnace when making the iron, and the other is '' tappings that runs out of a furnace at the end of the heat. As a general thing boilings are very much higher in phosphorus and silica than tappings. Mill cinder, as above outlined, is composed largely of protoxide of iron and silica. It contains, at times, ferric and magnetic oxides and is generally high in phosphorus. Table 9 is an analysis of four samples of mill cinder which the author secured to give an idea of the chemical composition of the same. As it would take about two tons of such cinder to make one ton of iron, there would be about twice the amount of phosphorus in the iron produced than is contained in the cinder ore where all cinder was used.
TAIJI.K 0.—ANALYSIS OF MILL CINDER.
i. 2. 3- 4-
Iron .......... .... S2-4-S 52.2O "52-91 53.70
Phosphorus . I .^2 * 7i/l •47 •37
Silica .................................... 24.65 2=5.06 23.43 2V ^9
Ma.njrdncsc . . . . ...... •34 •45 •57 •35
Iron mill cinder is only used for making foundry or nill iron. It ivS not used for making Bessemer for the reason that it would raise the phosphorus too high, which for foundry iron is not so objectionable;, in fact, foundry iron often requires high phosphorus. It can be said that a few are now using steel cinder in making
rosed to contain the most iron, followed in ordersent in the ore. Both these manganese metals are jf|V